Centrifugal air separators

ABSTRACT

Centrifugal air separators, systems including the same, and methods of separating gas are disclosed. Centrifugal air separators include a separation section configured to separate an input air stream into a clean air stream emitted from an exit port of the separation section and a waste stream emitted from a waste port of the separation section. The separation section includes a coiled duct and is configured to transmit through a duct entrance port a duct input air stream that is at least a portion of the input air stream and to at least partially separate the duct input air stream according to a molecular weight of components of the duct input air stream into a duct clean air stream that is at least a portion of the clean air stream and a duct waste stream that is at least a portion of the waste stream.

FIELD

The present disclosure relates to centrifugal air separators.

BACKGROUND

Purification of gases in air may be useful or vital in enclosedenvironments such as spacecraft, space habitats, submarines, undergroundmines, and terrestrial and non-terrestrial vehicles (e.g., aircraft,armored vehicles, and pressurized rovers). In particular, people producecarbon dioxide (CO₂) as a metabolic byproduct that can become noxious ifaccumulated within an enclosure. The average person exhales almost akilogram (kg) of carbon dioxide per day. In environments containinghigher levels of carbon dioxide, people may experience symptoms such asnausea, dizziness, and headaches. Hence, manned, enclosed environmentsneed a mechanism to remove carbon dioxide produced within theenvironment. Additionally, animals and plants are sensitive to the levelof carbon dioxide and would benefit from carbon dioxide control.

Two methods are commonly used to control the carbon dioxide level inmanned spacecraft—adsorption and chemical reaction. Chemical reactionsystems use chemicals (such as lithium hydroxide or potassiumsuperoxide) that react with carbon dioxide in the air to form benignproducts. These systems are one-time use. Once all of the chemical isreacted, no more carbon dioxide may be removed from the air. Chemicalreaction systems may use relatively little electrical power (e.g., tooperate a blower to direct air through a bed of the carbondioxide-reactive chemical) but do require a significant supply ofreplacement chemical. For example, a lithium hydroxide system requiresabout 1.5 kg of lithium hydroxide to remove the carbon dioxide producedby one person per day.

Adsorption systems are regenerative and thus do not have significantsupply requirements. Adsorption systems selectively adsorb carbondioxide under certain conditions and release carbon dioxide under otherconditions. For example, the International Space Station uses beds ofzeolite pellets that adsorb carbon dioxide from the air of the cabin andthat release the carbon dioxide when heated under vacuum (e.g., exposedto space vacuum). Because zeolites commonly preferentially adsorb watervapor over carbon dioxide, zeolite-based systems typically include aregenerative desiccant (e.g., a bed of silica gel) to remove water fromthe air to be exposed to the zeolites. Adsorption systems may usesignificant electrical power to regenerate the adsorbent bed and/or thedesiccant bed. Additionally, adsorption systems may be quite bulky andheavy. For example, the carbon dioxide removal systems on theInternational Space Station require about 1 kW (kilowatt) of power andthe adsorbent beds weigh about 48 kg each.

SUMMARY

Centrifugal air separators, systems including the same, and methods ofseparating gas are disclosed. Centrifugal air separators include a drivesection and a separation section. The drive section includes a blower.The drive section is configured to direct an input air stream from anatmosphere of an enclosure into an entrance port of the separationsection and the blower is configured to direct the input air streamthrough the separation section. The separation section is configured toseparate the input air stream into a clean air stream emitted from anexit port of the separation section and a waste stream emitted from awaste port of the separation section.

The separation section includes a coiled duct that has a duct entranceport fluidically connected to the entrance port of the separationsection, a duct exit port fluidically connected to the exit port of theseparation section, and a duct waste port fluidically connected to thewaste port of the separation section. Further, the coiled duct defines achannel between the duct entrance port and the duct exit port. The ductwaste port is proximate the duct exit port and fluidically connected tothe channel. The separation section is configured to transmit throughthe duct entrance port a duct input air stream that is at least aportion of the input air stream and to at least partially separate theduct input air stream according to a molecular weight of components ofthe duct input air stream into a duct clean air stream that is at leasta portion of the clean air stream and a duct waste stream that is atleast a portion of the waste stream.

Systems may be life support systems to support mammals living in anenclosure. For example, systems may include a carbon dioxide sensor, acentrifugal air separator, and a controller. The centrifugal airseparator includes a separation section with a plurality of coiledducts. Each of the coiled ducts has a duct entrance port fluidicallyconnected to the entrance port of the separation section, a duct exitport fluidically connected to the exit port of the separation section,and a duct waste port fluidically connected to the waste port of theseparation section. The separation section is configured to transmitthrough each duct entrance port a duct input air stream that is aportion of the input air stream. Each coiled duct is configured to atleast partially separate the duct input air stream according to amolecular weight of components of the duct input air stream into a ductclean air stream that is a portion of the clean air stream and a ductwaste stream that is a portion of the waste stream. Additionally, theseparation section includes a waste collection body that fluidicallyconnects the duct waste ports of the coiled ducts with the waste port ofthe separation section. The carbon dioxide sensor is configured to sensea partial pressure of carbon dioxide in an atmosphere of the enclosure.The controller is programmed to maintain a level of carbon dioxide inthe atmosphere of the enclosure at a partial pressure of less than 1 kPa(kilopascal) by controlling air flow through the centrifugal airseparator based upon the level of carbon dioxide in the atmosphere ofthe enclosure.

Methods may include recirculating clean air in an atmosphere of anenclosure. For example, methods may include directing an input airstream from the atmosphere of the enclosure through a number of coiledducts at a rate sufficient to stratify the input air stream within eachcoiled duct according to a molecular weight of components of the inputair stream and to form a heavy fraction stream and a light fractionstream. The heavy fraction stream is relatively enriched in carbondioxide as compared to the light fraction stream. Further, methods mayinclude withdrawing the heavy fraction stream from the number of coiledducts and returning the light fraction stream from the number of coiledducts to the atmosphere of the enclosure. Methods also may includedetermining a quantity related to a rate of production of carbon dioxidewithin the enclosure and maintaining a level of carbon dioxide in theatmosphere of the enclosure at a partial pressure of less than 1 kPa byselecting the number of coiled ducts based at least in part upon thequantity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a system that includes acentrifugal air separator.

FIG. 2 is a schematic representation of a centrifugal air separator.

FIG. 3 is a perspective view of an example of a separation section of acentrifugal air separator.

FIG. 4 is a schematic representation of a centrifugal air separator witha plurality of coiled ducts.

FIG. 5 is cross-sectional view of the interface between the drivesection and the separation section of FIG. 4, along the section line5-5.

FIG. 6 is a perspective view of an example of a centrifugal airseparator with a plurality of coiled ducts.

FIG. 7 is a schematic representation of methods of separating gas bymolecular weight.

DESCRIPTION

FIGS. 1-7 illustrate centrifugal air separators, systems including thesame, and methods of separating gas. In general, in the drawings,elements that are likely to be included in a given embodiment areillustrated in solid lines, while elements that are optional oralternatives are illustrated in dashed lines. However, elements that areillustrated in solid lines are not essential to all embodiments of thepresent disclosure, and an element shown in solid lines may be omittedfrom a particular embodiment without departing from the scope of thepresent disclosure. Elements that serve a similar, or at leastsubstantially similar, purpose are labeled with numbers consistent amongthe figures. Like numbers in each of the figures, and the correspondingelements, may not be discussed in detail herein with reference to eachof the figures. Similarly, all elements may not be labeled or shown ineach of the figures, but reference numerals associated therewith may beused for consistency. Elements, components, and/or features that arediscussed with reference to one or more of the figures may be includedin and/or used with any of the figures without departing from the scopeof the present disclosure.

FIG. 1 is a schematic representation of a system 10 that includes acentrifugal air separator 20. Systems 10 are configured to separate agas stream flowing through the system 10 into a light fraction streamand a heavy fraction stream according to the molecular weight of thecomponents of the gas stream. The system 10 may be, may be a portion of,or may include a gas separation system, a gas purification system, anair separation system, an air purification system, an environmentalcontrol system, an air recycling system, a carbon dioxide removalsystem, and/or a life support system. For example, system 10 may be alife support system to support mammals (e.g., humans), animals, and/orplants living in an enclosure 12.

System 10 may be included in, may be a component of, and/or may becoupled to an enclosure 12. Enclosures 12 define an enclosed space withan atmosphere 14. Enclosures 12 may be substantially sealed, completelysealed, or partially sealed such that gas (e.g., ‘fresh air’) fromoutside the enclosure 12 does not readily mix with the atmosphere 14 ofthe enclosure 12 and/or such that the atmosphere 14 does notsubstantially leak out of the enclosure 12. Examples of enclosures 12include spacecraft, space habitats, space suits, submarines,submersibles, underground mines, terrestrial vehicles (e.g., aircraft,armored vehicles), non-terrestrial vehicles (e.g., pressurized rovers),and greenhouses. Additionally or alternatively, enclosure 12 may be anopen enclosure such as an exhaust duct, flue, etc. that directs gas tothe system 10 and/or centrifugal air separator 20. For example, systems10 may be used for carbon dioxide scrubbing at refineries, power plants,cement plants, and/or chemical processing facilities.

The atmosphere 14 of the enclosure 12 typically is breathable andcomposed of similar gases as the Earth's atmosphere. Carbon dioxide andother gases may be confined within the enclosure 12 and/or producedwithin the enclosure 12. For example, people, which may be within theenclosure 12, generate about 1 kg of carbon dioxide per day per person.Additionally or alternatively, the atmosphere 14 may be a gascomposition with higher molecular weight components and lower molecularweight components. The higher molecular weight components may includecarbon dioxide and/or other higher molecular weight gases (e.g., tracecontaminants such as ethanol, acetone, toluene, etc.). The lowermolecular weight components may include beneficial and/or benigncomponents (at least in the sense of breathability) such as oxygen,water vapor, nitrogen, and/or argon. Though atmosphere 14 is breathableand includes carbon dioxide in most examples disclosed, atmosphere 14does not require carbon dioxide or breathable gases.

As schematically illustrated by the arced arrows in the enclosure 12 ofFIG. 1, the atmosphere 14 may circulate within the enclosure 12 and/orbe directed into the system 10 and/or the centrifugal air separator 20.

Centrifugal air separators 20 are configured to separate a gas streamflowing through the centrifugal air separator 20 into a light fractionstream and a heavy fraction stream according to the molecular weight ofthe components of the gas stream. Centrifugal air separators 20 includean entrance port 30 configured to accept the gas stream (the input airstream 31), an exit port 32 configured to emit the light fraction stream(the clean air stream 33), and a waste port 34 configured to emit theheavy fraction stream (the waste stream 35).

The naming of the centrifugal air separator 20, the input air stream 31,the clean air stream 33, the waste port 34, and the waste stream 35 isin accord with the use of the centrifugal air separator 20 in a lifesupport system or similar system. These terms are used for consistencyand clarity without implying a limitation on the use of the centrifugalair separator 20. Centrifugal air separators 20 are configured toseparate gas and are not necessarily limited to separating air.Centrifugal air separators 20 also may be referred to as gas separators,gas purifiers, air separators, air purifiers (e.g., centrifugal airpurifiers), air scrubbers (e.g., centrifugal air scrubbers), and/orcarbon dioxide removal apparatuses (e.g., centrifugal carbon dioxideremoval apparatuses). The input air stream 31 is a gas stream and is notnecessarily a stream of air. The input air stream 31 also may bereferred to as the input stream and/or the mixed gas stream. The cleanair stream 33 is the light fraction of gas output from the centrifugalair separator 20 and is not necessarily air or clean. The clean airstream 33 also may be referred to as the light fraction stream, thelower molecular weight output stream, the purified air stream, thepurified stream, and/or the primary output stream. The exit port 32,which is configured to emit the clean air stream 33, may be referred toas the light fraction port, the clean port, and/or the primary exitport. The waste stream 35 is the heavy fraction of gas output from thecentrifugal air separator 20 and is not necessarily waste, impurities,contamination, undesired gas, or unused gas. The waste stream 35 alsomay be referred to as the heavy fraction stream, the higher molecularweight output stream, the bleed stream, and/or the secondary outputstream. The waste port 34 is configured to emit the waste stream 35 andis not necessarily configured to emit waste, impurities, orcontamination. The waste port 34 may be referred to as the heavyfraction port, the bleed port, and/or the secondary exit port. Withoutimplying any particular use or limitation, ports and streams associatedwith other components are named according to their logical connection toentrance port 30, the input air stream 31, the exit port 32, the cleanair stream 33, the waste port 34, and/or the waste stream 35.

Centrifugal air separators 20 may include a plurality of entrance ports30, a plurality of exit ports 32, and/or a plurality of waste ports 34.Each port of the plurality of ports may have an independent gas streamand the total flow through all of the ports of a plurality of ports maybe referred to as the total, or collective, gas stream (e.g., thecollective input stream, the collective primary output stream, and thecollective waste stream).

The input air stream 31 is a sample of the atmosphere 14 (or other gassource). The clean air stream 33 has less (by mass and/or concentration)higher molecular weight components than the input air stream 31. Thewaste stream 35 has more (by mass and/or concentration) higher molecularweight components than the input air stream 31. Thus, the waste stream35 may be relatively enriched in higher molecular weight components ascompared to the input air stream 31 and/or the clean air stream 33.Similarly, the clean air stream 33 may be relatively depleted in highermolecular weight components as compared to the input air stream 31and/or the waste stream 35. The clean air stream 33 may have more (bymass and/or concentration) lower molecular weight components than theinput air stream 31. The waste stream 35 may have less (by mass and/orconcentration) lower molecular weight components than the input airstream 31. Thus, the waste stream 35 may be relatively depleted in lowermolecular weight components as compared to the input air stream 31and/or the clean air stream 33. Similarly, the clean air stream 33 maybe relatively enriched in lower molecular weight components as comparedto the input air stream 31 and/or the waste stream 35.

Higher molecular weight components may include gases with a molecularweight (M.W.) greater than or equal to a threshold such as a molecularweight of 36, 38, 40, 42, or 44. Such thresholds may differentiate mostbeneficial and benign gases in a breathable atmosphere (e.g., watervapor (M.W. 18), nitrogen (M.W. 28), oxygen (M.W. 32), and argon (M.W.40)) from carbon dioxide (M.W. 44) and higher molecular weight(potentially contaminant) gases. As an example, for an input air stream31 that includes oxygen, water vapor, nitrogen, and carbon dioxide, thehigher molecular weight components may include carbon dioxide while thelower molecular weight components may include oxygen, water vapor, andnitrogen.

The waste stream 35 may include carbon dioxide and/or heaviercomponents. Further, the waste stream 35 may consist primarily of carbondioxide and/or heavier components. The clean air stream 33 may includecomponents lighter than the primary components of the waste stream 35.For example, the clean air stream 33 may include components such asoxygen and/or water vapor, which are lighter than carbon dioxide.Because, the centrifugal air separator 20 is configured to separate theinput air stream 31 according to the molecular weight of the components,carbon dioxide may be separated from oxygen and water vapor withoutfirst desiccating the input air stream 31.

Systems 10 and/or centrifugal air separators 20 may be configured todischarge a waste stream 35 consisting primarily of higher molecularweight components and little to none of the lower molecular weightcomponents of the input air stream 31. For an isolated enclosed system,such as a spacecraft, conservation of the atmosphere 14 is an importantconsideration. Hence, systems 10 and/or centrifugal air separators 20may be configured to remove carbon dioxide (discharged in the wastestream 35) while removing little to none of the beneficial and/or benigncomponents of the atmosphere 14. The beneficial and/or benign componentswould be discharged back into the atmosphere 14 as the clean air stream33. For example, the waste stream 35 may include carbon dioxide andlittle to none of oxygen, nitrogen, and/or water vapor while the cleanair stream 33 may include substantially the same level of oxygen,nitrogen, and/or water vapor as the input air stream 31.

Though the example of FIG. 1 illustrates that the exit port 32 may beconfigured to emit the clean air stream 33 into the atmosphere 14 of theenclosure 12, the clean air stream 33 may be emitted directly orindirectly into the atmosphere 14, may be reacted, mixed, or otherwisemodified, and/or may be accumulated in a vessel. Also, though theexample of FIG. 1 illustrates that the waste port 34 may be configuredto emit the waste stream 35 out of the enclosure 12 (e.g., vented‘overboard’ a spacecraft), the waste stream 35 may be expelled from theenclosure 12, may be reacted, mixed, or otherwise modified, and/or maybe accumulated in a vessel.

Centrifugal air separators 20 may be configured to emit the clean airstream 33 and the waste stream 35 at a mass flow ratio of the clean airstream 33 to the waste stream 35 of at least 1:1, at least 2:1, at least5:1, at least 10:1, at least 100:1, or at least 1000:1. Generally, themass flow ratio may be related to the area ratio of the exit port 32 andthe waste port 34. Where a centrifugal air separator 20 has a pluralityof exit ports 32 and/or a plurality of waste ports 34, the mass flowratio and the area ratio may be formed using the total flow or area,respectively, of all of the respective ports. Centrifugal air separators20 may be configured such that the clean air stream 33 to waste stream35 mass flow ratio (the light fraction stream to heavy fraction streammass flow ratio) may be substantially the same as the ratio (and/or theexpected ratio) of the light fraction components to the heavy fractioncomponents in the input air stream 31 (the input stream). For example,the clean air stream 33 to waste stream 35 mass flow ratio may be about400%, about 200%, about 150%, about 110%, about 100%, about 90%, about70%, about 50%, about 20%, or about 10% of the ratio (and/or theexpected ratio) of the light fraction components to the heavy fractioncomponents in the input air stream 31.

Because centrifugal air separators 20 operate by separating the inputair stream 31 as the stream travels through the centrifugal airseparator 20, the centrifugal air separator 20 may be operatedsubstantially continuously. Unlike adsorption systems, no regenerationof a centrifugal air separator 20 is required. Though no specific downtime is required to discharge carbon dioxide or other accumulated gases,centrifugal air separators 20 may be taken out of service forconvenience, maintenance, cleaning, etc. For example, particulate and/oraerosols within the input air stream 31 may accumulate within thecentrifugal air separator 20 and may be removed, for example, byflushing the centrifugal air separator 20 with a solvent and/or backflushing a clean gas through the centrifugal air separator 20 (e.g.flushing gas from the exit port 32 and/or the waste port 34 to theentrance port 30).

Systems 10 and/or centrifugal air separators 20 may include an inputfilter, a carbon dioxide sensor 16, a controller 18, a gas sensor, anoxygen source, an oxygen sensor, a heater, a water recovery system, awater production system, and/or a humidity control apparatus. Forexample, input filters may be configured to remove and/or reduceparticulates and/or suspended liquids (e.g., mists, aerosols, waterdrops, etc.) from the input air stream 31 and/or from the interior ofthe centrifugal air separator 20.

Carbon dioxide sensors 16 are devices configured to detect the presence,amount, partial pressure, and/or concentration of carbon dioxide in agas. Carbon dioxide sensors 16 may be configured to sense carbon dioxidein the atmosphere 14 of the enclosure 12, the input air stream 31, theclean air stream 33, the waste stream 35, and/or within the centrifugalair separator 20. Examples of carbon dioxide sensors 16 includenon-dispersive infrared carbon dioxide sensors (measurement by infraredabsorbance), chemical carbon dioxide sensors (measurement by chemicalreaction), MEMS (microelectromechanical system) sensors (measurement bychanges in mechanical resonance and/or deflection), and massspectrometers.

Controllers 18 may be configured to control the operation of the system10 and/or the centrifugal air separator 20. For example, the controller18 may be programmed to perform any of the methods described furtherherein. The controller 18 may be programmed to control air flow throughthe centrifugal air separator 20, optionally based upon a carbon dioxidelevel as may be sensed by carbon dioxide sensor 16 and/or inferred byanother sensor (e.g., measuring oxygen levels in the clean air stream 33and/or the waste stream 35 as a proxy for the efficiency of separation).The controller 18 may be programmed to control the rate of separation ofcarbon dioxide (or other gas constituents such as a higher molecularweight gas) in the centrifugal air separator 20. The controller 18 maybe programmed to maintain a carbon dioxide level (e.g., a concentrationor a partial pressure) in the atmosphere 14 below a threshold level. Thethreshold level may be a threshold deemed safe for human exposure, safefor human habitation, and/or comfortable to humans living within theenclosure 12. For example, the threshold may be less than 1 kPa (about7.5 mmHg (millimeters of mercury)), less than 0.8 kPa (about 6 mmHg),less than 0.6 kPa (about 4.5 mmHg), less than 0.4 kPa (about 3 mmHg),less than 0.3 kPa (about 2 mmHg), about 0.5 kPa (about 4 mmHg), about0.3 kPa (about 2 mmHg), and/or about 0.2 kPa (about 1 mmHg).

Controllers 18 may be any suitable device or devices that are configuredto perform the functions discussed herein. For example, controllers mayinclude one or more of an electronic controller, a dedicated controller,a special-purpose controller, a computer, a special-purpose computer, adisplay device, a logic device, a memory device, and/or a tangiblecomputer-readable medium suitable for storing computer-executableinstructions for implementing one or more aspects of systems and/ormethods according to the present disclosure.

FIG. 2 schematically represents details of centrifugal air separators20. Centrifugal air separators 20 include at least one drive section 22and at least one separation section 24. Drive sections 22 have a drivesection entrance port 28 and a drive section exit port 36. Separationsections 24 have an entrance port 40 (also called a separation sectionentrance port), an exit port 42 (also called a separation section exitport) and a waste port 44 (also called the separation section wasteport). Separation sections 24 may include a plurality of entrance ports40, a plurality of exit ports 42, and/or a plurality of waste ports 44.Generally, the waste port(s) 44 of the separation section 24 is (are)fluidically connected to at least one of the waste ports 34 of thecentrifugal air separator 20. One or more of the waste ports 44 may beconfigured to form at least a portion of the waste port(s) 34 of thecentrifugal air separator 20.

The drive section(s) 22 and the separation section(s) 24 of acentrifugal air separator 20 are connected such that gas (e.g., air) mayflow from the entrance port 30 to the exit port 32 through the drivesection(s) 22 and the separation section(s) 24. These sections aregenerally connected serially, with one section upstream (i.e., closer tothe entrance port 30) of another. Where the centrifugal air separator 20includes one drive section 22 and one separation section 24, one of thedrive section 22 or the separation section 24 is located upstream of theother, i.e., gas flow generally travels from the drive section 22 to theseparation section 24 or vice versa. The entrance port of the mostupstream of the sections may be the entrance port 30 of the centrifugalair separator 20. The exit port of the most downstream of the sectionsmay be the exit port 32 of the centrifugal air separator 20.Intermediate entrance port(s) and exit port(s) of the sections arefluidically connected end-to-end to form a continuous fluid path fromthe entrance port 30 to the exit port 32. For example, in FIG. 2, thedrive section 22 is upstream of the separation section 24. The entranceport 28 of the drive section 22 is also the entrance port 30 of thecentrifugal air separator 20. The exit port 36 of the drive section 22is fluidically connected to the entrance port 40 of the separationsection 24. The exit port 42 of the separation section 24 is also theexit port 32 of the centrifugal air separator 20.

Drive sections 22 are configured to direct the input air stream 31 fromthe atmosphere 14 of the enclosure 12 into the entrance port 30 and/orthrough the separation section(s) 24 (from the entrance port 40 to theexit port 42). Drive sections 22 may include a blower 26 (which also maybe called a compressor, a pump, and/or a fan) that is configured todirect the input air stream 31 from the entrance port 30 through theseparation section 24 (from the entrance port 40 to the exit port 42).Drive sections 22 and/or blowers 26 may be configured to drive the air(or other gas compositions) from the entrance port 30 to the exit port32. Additionally or alternatively, drive sections 22 and/or blowers 26may be configured to draw gas from the entrance port 30 to the exit port32. For example, FIG. 2 schematically illustrates the drive section 22between the entrance port 30 and the separation section 24 (i.e.,generally upstream of the separation section 24). In this arrangement,the drive section 22 is generally configured to draw the input airstream 31 into the entrance port 30 and to drive the input air stream 31through the separation section 24. Alternatively, the drive section 22may be generally downstream of the separation section 24, e.g., betweenthe separation section 24 and the exit port 32. Further, the centrifugalair separator 20 may include more than one drive section 22, forexample, one upstream of the separation section 24 and one downstream ofthe separation section 24. Additionally or alternatively, drive sections22 may include, and/or may be, a source of pressurized gas from a vesseland/or another system.

Centrifugal air separators 20 may include a vacuum source 80 to draw thewaste stream 35 from the waste port 34. The vacuum source 80 may includea vacuum pump and/or a vacuum vessel. Additionally or alternatively, thevacuum source 80 may be selectively fluidically coupled to a vacuumexterior to the enclosure 12 (e.g., the vacuum of space outside aspacecraft). The vacuum source 80 may be configured to apply asub-atmospheric pressure to the waste port 34, for example a pressureless than 100 kPa, less than 80 kPa, less than 50 kPa, or less than 10kPa. Additionally or alternatively, the centrifugal air separator 20and/or the vacuum source 80 may be configured to apply a negativepressure differential from the waste port 34 to the channel 56 proximatethe waste port 34. For example, the pressure at the waste port 34 may beat least 10 kPa, at least 25 kPa, or at least 50 kPa less than thepressure in the channel 56 proximate the waste port 34. The pressuredifferential between the waste port 34 and the channel 56 may be asgreat as the absolute pressure in the channel 56.

Separation sections 24 are configured to separate a gas stream flowingthrough the separation section 24 into a light fraction stream emittedat the exit port 42 and a heavy fraction stream emitted at the wasteport 44 according to the molecular weight of the components of the gasstream.

Centrifugal air separators 20 may include more than one stage of gasseparation, the first stage being as described, including a drivesection 22 and a separation section 24. An optional second-stage section68 (also called a secondary section and a subsequent-stage section) isconfigured to further separate the gas output from the first stage,and/or prior stages. The second-stage section 68 has an entrance port70, an exit port 72, and a waste port 74. The second-stage section 68 isconfigured to accept at least a portion of one of the clean air stream33 or the waste stream 35 into the entrance port 70 as a second-stageinput stream 71 and is otherwise configured like a separation section24. For example, the second-stage section 68 is configured to separatethe input stream 71 of the second-stage section 68 into a second-stageclean air stream 73 (also called a second-stage light fraction stream)and a second-stage waste stream 75 (also called a second-stage heavyfraction stream), the second-stage clean air stream 73 being dischargedfrom the exit port 72 and the second-stage waste stream 75 beingdischarged from the waste port 74. Further secondary sections, whenpresent, are configured likewise, with the first stage feeding thesecond stage which feeds the third stage, etc.

To further purify the waste stream 35 (e.g., to increase the amountand/or concentration of the heavier molecular weight components in thestream), the waste stream 35 may be input into the entrance port 70 ofthe second-stage section 68, i.e., the waste port 34 may be fluidicallyconnected to the entrance port 70. To further purify the clean airstream 33 (e.g., to increase the amount and/or concentration of thelighter molecular weight components in the stream), the clean air stream33 may be input into the entrance port 70 of the second-stage section68, i.e., the clean air port 32 may be fluidically connected to theentrance port 70. To remove carbon dioxide as a waste gas from abreathable atmosphere, the waste stream 35 may be directed into theentrance port 70, the clean air stream 33 and the second-stage clean airstream 73 may be discharged into the atmosphere 14, and the second-stagewaste stream 75 may be handled as would be the waste stream 35 in theabsence of the second stage 68. By purifying the waste stream 35 ratherthan the clean air stream 33 with the second-stage section 68, more ofthe benign and beneficial components of the breathable atmosphere 14 maybe recovered and recycled back into the atmosphere 14.

The second-stage section 68 and/or the centrifugal air separator 20 mayinclude a drive section 22 configured to direct air (or a gas stream)through the second-stage section 68. This drive section 22 may beconfigured to drive and/or to draw air through the second-stage section68.

Separation sections 24 and optional second-stage sections 68 include atleast one coiled duct 48 (which also may be referred to as a spiral ductand/or a helical duct). Coiled ducts 48 have an entrance port 50 (alsocalled a duct entrance port), an exit port 52 (also called a duct exitport), and at least one waste port 54 (also called a duct waste port).Coiled ducts 48 may include a plurality of entrance ports 50, aplurality of exit ports 52, and/or a plurality of waste ports 54.

Coiled ducts 48 define a channel 56 between the entrance port 50 and theexit port 52. The channel 56 also may be called the interior of thecoiled duct 48. Coiled ducts 48 may be substantially tubular, in whichcase, the exterior of the coiled duct may mimic many of the features ofthe channel 56. However, coiled ducts 48 may define all or a portion ofthe channel 56 within a body that is not tubular.

The entrance port 50 of each of the coiled ducts 48 of a section (theseparation section 24 or the second-stage section 68) is fluidicallyconnected to the entrance port of the corresponding section (theentrance port 40 of the separation section 24 or the entrance port 70 ofthe second-stage section 68) and may be configured to form at least aportion of the entrance port of the corresponding section. The exit port52 of each of the coiled ducts 48 of a section is fluidically connectedto the exit port of the corresponding section (the exit port 42 of theseparation section 24 or the exit port 72 of the second-stage section68) and may be configured to form at least a portion of the exit port ofthe corresponding section. The one or more waste ports 54 of each of thecoiled ducts 48 of a section are fluidically connected to the waste portof the corresponding section (the waste port 44 of the separationsection 24 or the waste port 74 of the second-stage section 68). Thus,the coiled ducts 48 of a section are configured to operate in parallelwithin a section.

Coiled ducts 48 are configured to separate a gas stream (also referredto as a duct input gas stream) flowing into the entrance port 50 into alight fraction stream emitted at the exit port 52 and a heavy fractionstream emitted at the waste port 54 according to the molecular weight ofcomponents of the gas stream. The light fraction stream and the heavyfraction stream together are essentially the only gas output from thecoiled duct 48. That is, coiled ducts 48 may emit only incidentalamounts of gas besides the light fraction stream and the heavy fractionstream. The gas flow of the input gas stream and the light fractionstream are substantially the same. The gas flow of the heavy fractionstream is a small fraction of the total gas flow emitted by the coiledduct 48. For example, the flow of the heavy fraction stream may be lessthan 10%, less than 1%, or less than 0.1% of the flow of the lightfraction stream.

Each separation section 24 and second-stage section 68 is configured totransmit at least a portion of the gas stream input to the section intothe coiled duct 48 (into the entrance port 50), to transmit from theexit port of the section at least a portion of the light fraction streamemitted by the coiled duct 48 (from the exit port 52), and to transmitfrom the waste port of the section at least a portion of the heavyfraction stream emitted by the coiled duct 48 (from the waste port 54).Hence, the light fraction stream emitted from the coiled duct 48 may becalled the duct clean air stream and the heavy fraction stream emittedfrom the coiled duct 48 may be called the duct waste stream.

Coiled ducts 48 are configured to separate components of the duct inputgas stream according to the molecular weight of the components bydirecting the gas stream along the coiled channel 56 and therebysubjecting the gas to centrifugal force. The channel 56 is configured tostratify gas travelling through the channel 56 according to themolecular weight of the components of the gas due to the centrifugalforce imparted on the gas as it travels the coiled channel 56.

Coiled ducts 48 and channels 56 are configured to flow the duct inputgas stream in a generally laminar manner, i.e., in a manner where theturbulence of the flow is low enough and/or directed (e.g., confined toparticular layers and/or regions) to permit stratification of the gasstream in a direction perpendicular to the average gas flow. Thegenerally laminar manner may be influenced by speed (e.g., velocity,mass flow rate) of the gas flow, gas parameters (e.g., pressure,temperature, and viscosity), the shape of the channel 56, the interiorprofile of the channel 56, and the surface characteristics of theinterior of the channel 56. Lower speeds and higher viscosity tend toencourage reduced turbulence. However, higher speeds tend to increasethe centrifugal force. Smaller dimensions tend to encourage reducedturbulence.

Suitable gas flow through coiled ducts 48 and centrifugal air separators20 may be at a velocity, mass flow rate, temperature, and/or pressureselected to stratify the gas within the coiled duct 48. The velocity ofthe gas flow may be at least 10 m/s (meters per second), at least 20m/s, or at least 50 m/s. The mass flow rate of the gas flow may be atleast 0.1 g/s (grams per second), at least 0.5 g/s, at least 2 g/s, orat least 5 g/s. The temperature of the gas flow may be selected to benon-condensing and/or near standard room temperature (e.g., 0° C.-50°C.). The temperature of the gas flow through a coiled duct 48 mayincrease as the gas flows through the coiled duct 48, e.g., due tofriction of the gas flow. The coiled ducts 48 may include and/or may bein thermal contact with heat sinks, chillers, and/or heat exchangers tomaintain, increase, and/or decrease the temperature of the gas flow asit flows through the coiled duct 48. The pressure of the input gas flowmay be selected to be near standard atmospheric pressure (e.g., 70-110kPa), at the pressure induced by the drive section 22, which may behigher or lower than standard atmospheric pressure, and/or at thepressure of a gas source used in addition to or as an alternative to thedrive section 22. Centrifugal air separators 20 and/or coiled ducts 48may be configured to produce a pressure differential between theentrance port 30 and the exit port 32 and/or between the duct entranceport 50 and the duct exit port 52 of less than 100 kPa, less than 60kPa, or less than 30 kPa when gas is flowing with a mass flow rate of2.5 g/s from the respective entrance port.

The profile of the channel 56 (e.g., as characterized by its effectivediameter) may be substantially uniform along the channel 56, may tapertoward the duct entrance port 50, or may taper toward the duct exit port52. The profile of the channel 56 may be substantially circular,substantially elliptical, substantially ovate, and/or rounded. Theaverage effective diameter of the channel 56 may be at least 0.1 cm(centimeters), at least 0.2 cm, at least 0.5 cm, at least 1 cm, at most100 cm, at most 50 cm, at most 20 cm, at most 10 cm, at most 5 cm,and/or at most 2 cm.

Coiled ducts 48 and channels 56 may include a coiled portion, a spiralportion, and/or a helical portion in which the channel 56 is coiled,spiral, and/or helical, respectively. Coiled ducts 48 and channels 56may include a series of loops, for example, at least 5, at least 10,less than 50, and/or less than 100 loops. The loops may be, and/or mayinclude one or more portions that are, substantially helical and/orsubstantially spiral. Loop shapes generally are smooth. Abrupt changesin the direction of the channel 56 may induce turbulence into the gasflow. Larger (looser) loops tend to contribute to smoother air flow,while smaller (tighter) loops tend to induce greater centrifugal forcein the gas. The effective diameter of a series of loops may besubstantially uniform, tapered toward the duct entrance port 50, ortapered toward the duct exit port 52. The average effective diameter ofa series of loops may be at least 1, at least 2, at least 3, at least 5,at most 10, and/or at most 5 times the average effective diameter of thechannel 56. Two or more of the loops may be essentially in contact witheach other (e.g., the portions of the channel 56 within the loops may beseparated by a shared wall). Additionally or alternatively, two or moreof the loops may be spaced apart from each other, for example, by atleast 0.1, at least 0.5, at least 1, at most 10, and/or at most 5 timesthe average effective diameter of the channel 56.

Coiled ducts 48 and/or channels 56 may be sized to remove a selected gasin the waste stream 35 at a specified rate. For example, coiled ducts 48and/or channels 56 may be sized to remove carbon dioxide from the inputair stream 31 at a rate comparable to the rate of production within theenclosure 12. Sizing of the coiled ducts 48 and/or the channels 56 mayinclude selecting the channel area, the channel effective diameter, thechannel profile, the channel length, the coil (loop) curvature, thenumber of loops, the area of the duct entrance port 50, the area of theduct exit port 52, the area of the duct waste port(s) 54, and/or theplacement of the duct waste port(s) 54. For carbon dioxide, the targetrate of removal may be less than 0.1 g/s (about 10 kg per day), lessthan 0.03 g/s, less than 0.01 g/s, less than 0.003 g/s, or less than0.001 g/s. For example, separation sections 24 may be configured toremove carbon dioxide at a target removal rate (e.g., the rate ofproduction within the enclosure 12). Hence, a coiled duct 48 in aseparation section 24 with a single coiled duct 48 may be sized toremove carbon dioxide at the target removal rate. Each coiled duct 48 ina separation section 24 with a plurality of coiled ducts 48 may be sizedto remove carbon dioxide at a portion (e.g., an equal portion) of thetarget removal rate.

Coiled ducts 48 may include and/or may be composed of suitably resilientand gas tight materials such as metal, plastic, glass, etc. Coiled ducts48 may be configured to be substantially gas impermeable under operatingconditions (with gas flowing as described herein, e.g., at aboutstandard pressure (about 100 kPa) and temperature (about 20° C.)).Coiled ducts 48 may be, or include portions that are, rigid, flexible,heat conductive, and/or heat insulating. Coiled ducts 48 and/orcentrifugal air separators 20 may include vibration dampening materialsand/or insulation to reduce vibrations in the coiled ducts 48 and/or toisolate vibrations of the coiled ducts 48 from the environment outsidethe centrifugal air separators 20.

FIG. 3 illustrates an example of a coiled duct 48 that is tubular andthat defines a substantially helical channel 56. Coiled ducts 48 areconfigured with a principal direction 90 of gas flow that is thedirection from the entrance port 50 to the exit port 52. In the exampleof FIG. 3, the principal direction 90 is the direction along the axis ofthe helix from the entrance port 50 to the exit port 52 (also indicatedas the z-axis). The channel 56 may be described in terms of a leadingedge region 60 and a trailing edge region 62 with respect to theprincipal direction 90, as indicated at the opening of the channel 56 atthe exit port 52 in FIG. 3. The leading edge region 60 of the channel 56is the forward region with respect to the principal direction 90 (theedge region toward the exit port 52). The trailing edge region 62 of thechannel 56 is the rearward region with respect to the principaldirection 90 (the edge region toward the entrance port 50). Though theedge regions are only indicated for the opening of the channel 56 at theexit port 52, any cross section or profile of the channel 56 may becharacterized with a leading edge region 60 and a trailing edge region62, unless the channel 56 happens to be parallel to the principaldirection 90. Thus, each loop of the channel 56 may be described with aleading edge region 60 that faces forward with respect to the principaldirection 90 and a trailing edge region 62 that faces rearward withrespect to the principal direction 90.

Further, the channel 56 may be described in terms of an outside edgeregion 64 and an inside edge region 66 with respect to the loops. Theoutside edge region 64 of the channel 56 is the edge region along theoutside of the curvature of the channel 56 (i.e., along the outside ofthe loops). The inside edge region 66 of the channel 56 is the edgeregion along the inside of the curvature of the channel 56 (i.e., alongthe inside of the loops). For a channel 56 with substantially parallelwalls, the outside edge region 64 has a larger radius of curvature thanthe inside edge region 66. In FIG. 3, the direction that distinguishesthe outside edge region 64 from the inside edge region 66 is indicatedas the x-direction.

As gas flows through the channel 56, the gas experiences a centrifugalforce generally in the x-direction (i.e., away from the local center ofcurvature of the channel 56). In some flow conditions and channelconfigurations, gas may stratify along the x-direction (with heaviercomponents generally drawn toward the outside edge region 64). In someflow conditions and channel configurations, gas may stratify along theprincipal direction 90 (with heavier components generally drawn towardthe leading edge region 60). Hence, the channel 56 may be configured tostratify the gas along the x-direction, the principal direction 90 (thez-direction), and/or a direction between the x-direction and theprincipal direction 90. The channel 56 may be configured to concentrateheavier gases along the leading edge region 60, the outside edge region64, and/or an edge region from the leading edge region 60 to the outsideedge region 64.

All of the one or more waste ports 54 of the coiled duct 48 areproximate the exit port 52 of the coiled duct 48. The waste port(s) 54may be fluidically connected to the channel 56 in an end region of thechannel 56. The end region of the channel 56 may be less than 20%, lessthan 10%, or less than 5% of the length of the channel 56. The endregion may be the last 20%, 10%, or 5% of the loops of the channel 56(e.g., the last 5, 4, 3, 2, or 1 loops). The waste port(s) 54 of thecoiled duct 48 may be fluidically connected to the channel 56 within theleading edge region 60, the outside edge region 64, and/or between theleading edge region 60 and the outside edge region 64. For example, FIG.3 illustrates several optional waste ports 54 generally within theleading edge region 60. The connection of the waste ports 54 may beexclusively in the leading edge region 60, the outside edge region 64,and/or between the leading edge region 60 and the outside edge region64. For example, the waste port(s) 54 of the coiled duct 48 may befluidically connected to the channel 56 only within the leading edgeregion 60. As another example, the waste port(s) 54 of the coiled duct48 may be fluidically connected to the channel 56 only within theoutside edge region 64.

Coiled ducts 48 may be configured to emit the duct clean air stream andthe duct waste stream at a mass flow ratio of the duct clean air streamto the duct waste stream of at least 1:1, at least 2:1, at least 5:1, atleast 10:1, at least 100:1, or at least 1000:1. Generally, the mass flowratio may be related to the area ratio of the exit port 52 and the wasteport(s) 54. Where a coiled duct 48 has a plurality of waste ports 54,the mass flow ratio and the area ratio may be formed using the totalflow or area, respectively, of the waste ports 54. Each waste port 54may have an effective diameter that is less than 50%, less than 20%,less than 10%, less than 3%, or less than 1% of the effective diameterof the channel 56 proximate the waste port 54. Each waste port 54 mayhave an effective diameter that is less than 50%, less than 20%, lessthan 10%, less than 3%, or less than 1% of the effective diameter of theexit port 52. Though relatively small, waste ports 54 are apertures,passages, channels, or the like that are large enough to transmit gas ofthe heavy fraction stream. Waste ports 54 may have an effective diametergreater than 0.001 mm (millimeters), greater than 0.01 mm, or greaterthan 0.1 mm.

As shown in the examples of FIGS. 2 and 4, separation sections 24 andsecond-stage sections 68 may include a waste collection body 46 that isconfigured to collect and/or to combine waste stream(s) (heavy fractionstreams) from the coiled duct(s) 48 (emitted by the waste port(s) 54)and to direct the collected waste gas to the waste port 44 or thesecond-stage waste port 74, respectively. The waste collection body 46generally fluidically connects one or more of the waste ports 54 of thecoiled duct(s) 48 to the respective waste port 44 or second-stage wasteport 74. The waste collection body 46 may define the respective wasteport 44 or second-stage waste port 74. The waste collection body 46 maydefine a passage from the waste port(s) 54 of the coiled duct(s) 48 tothe respective waste port 44 or second-stage waste port 74. The wastecollection body 46 may define a volume that contains at least a portionof the coiled duct proximate the waste port(s) 54. The waste collectionbody 46 may substantially cover and/or form a sheath over the coiledduct(s) 48. Alternatively, the waste collection body 46 may onlysubstantially cover the waste port(s) 54.

As shown in the example of FIG. 4, separation sections 24 may include aplurality of coiled ducts 48. Generally, the coiled ducts 48 areconfigured to operate (separate gas) in parallel and each is configuredto operate on a portion of the input air stream 31. Each of the coiledducts 48 may be substantially identical, configured for substantiallythe same input gas flow, and/or configured for substantially the samewaste gas flow (i.e., heavy fraction flow). The centrifugal airseparator 20 may include an optional input manifold configured to dividethe input air stream among the plurality of coiled ducts 48. The inputmanifold may be configured to substantially evenly split the input airstream among the coiled ducts 48. The centrifugal air separator 20 mayinclude an optional output manifold configured to combine the lightfraction output streams (the clean air streams) of the plurality ofcoiled ducts into the clean air stream 33.

Second-stage sections 68 may include a plurality of coiled ducts 48 inthe same manner that separation sections 24 may include a plurality ofcoiled ducts 48. However, second-stage sections 68 do not necessarilyhave the same number or configuration of coiled ducts 48 as thecorresponding separation section 24 of the centrifugal air separator 20.

Where a separation section 24 of a centrifugal air separator 20 has aplurality of coiled ducts 48, the drive section(s) 22 of the centrifugalair separator 20 may be configured to direct gas through each of theentrance ports 50 of the coiled ducts 48, for example, driving gasand/or drawing gas from each of the entrance ports 50 to the respectiveexit ports 52. Drive sections 22 may serve one or more of the pluralityof coiled ducts 48. For example, centrifugal air separators 20 mayinclude a drive section 22 for each coiled duct 48. Alternatively,centrifugal air separators 20 may include a single drive section 22 todirect gas through all of the plurality of coiled ducts 48. Similarly, adrive section 22 may include one or more blowers 26 that serve one ormore coiled ducts 48. For example, a drive section 22 may include oneblower 26 for each coiled duct 48. As another example, a drive section22 may include a single blower 26 for all of the coiled ducts 48 servedby the drive section 22.

FIG. 5 illustrates the interface between the drive section 22 and theseparation section 24 shown in FIG. 4 (and as indicated by section line5-5). Specifically, FIG. 5 shows the entrance port 40 of the separationsection 24 configured to group the entrance ports 50 of the plurality ofcoiled ducts 48 towards the center of the separation section 24. Thedrive section exit port 36 may be configured to direct gas substantiallyonly through the entrance ports 50 of the coiled ducts.

Further, FIG. 5 illustrates the packing of 4 similar-sized coiled ducts48 together within a single waste collection body 46 that substantiallyencloses the coiled ducts 48. The coiled ducts 48 are arranged asparallel helical coils packed nearly in contact with each other. Aplurality of coiled ducts 48 may be interleaved and/or nested to reducethe total volume used by the separation section 24 (or second-stagesection 68).

The trailing edge regions 62 of the coiled ducts 48 of FIG. 5 arevisible from the entrance port 40. For reference, the outside edgeregions 64 and the inside edge regions 66 of each of the coiled ducts 48are indicated. From the view of FIG. 5, the leading edge regions 60 ofeach of the coiled ducts 48 would be below each loop toward the exitport 42.

FIG. 6 illustrates an example of a centrifugal air separator 20 with aplurality of coiled ducts 48 in the separation section 24. Additionally,the exit port 42 of the separation section 24 (which is the exit port 32of the centrifugal air separator 20) is illustrated. The exit port 42 isconfigured to expose the exit ports 52 of the coiled ducts 48. The wasteports 54 of the coiled ducts 48 are enclosed within the waste collectionbody 46 (which is illustrated as transparent). The waste ports 54 areshown in the leading edge regions 60 of the coiled ducts 48.

FIG. 7 schematically represents methods 100 according to the presentdisclosure. Methods 100 generally are methods of separating gas such asrecirculating clean air in an atmosphere of an enclosure by separatingcarbon dioxide or other higher molecular weight components such ascontaminants.

Methods 100 include directing 102 an input stream of gas (such as inputair stream 31) through a coiled duct (such as coiled duct 48) tocentrifugally separate the gas according to the molecular weight ofcomponents of the gas into a light fraction stream and a heavy fractionstream. For applications such as purifying air for life support,reducing/maintaining the concentration of carbon dioxide within anenclosure, and/or recycling the atmosphere within an enclosure, theheavy fraction stream may be relatively enriched in carbon dioxide ascompared to the light fraction stream. Directing 102 may includedirecting input air from the atmosphere of an enclosure through thecoiled duct at a rate to stratify the air within the coiled duct.Directing 102 may include directing the input stream of gas through thecentrifugal air separator 20.

Methods 100 may include withdrawing 104 the heavy fraction stream (suchas the waste stream 35) from the coiled duct, for example to direct theheavy fraction stream away from the coiled duct. For applications suchas purifying air for life support and/or reducing/maintaining theconcentration of carbon dioxide within an enclosure, the heavy fractionstream may be accumulated, e.g., in a vessel, and/or directed out of theenclosure, e.g., overboard a spacecraft, into a vessel, and/or to achemical processing system (such as a water production system).

Methods 100 may include accumulating the light fraction stream and/orusing the light fraction stream. For applications such as purifying airfor life support and/or recycling the atmosphere within an enclosure,methods 100 may include returning 106 the light fraction stream from thecoiled duct to the atmosphere of the enclosure.

Methods 100 may include sensing a concentration and/or a partialpressure of carbon dioxide in the atmosphere of an enclosure, the inputstream of gas, the heavy fraction stream, and/or the light fractionstream.

Methods 100 may include determining a quantity related to a rate ofproduction of carbon dioxide within an enclosure. The quantity may be anumber of people within the enclosure, a level of carbon dioxide in theatmosphere of the enclosure, a level of carbon dioxide in the inputstream, a level of carbon dioxide in the heavy fraction stream, a levelof carbon dioxide in the light fraction stream, and the rate ofproduction of carbon dioxide within the enclosure. Methods 100 mayinclude selecting the number of coiled ducts based at least in part uponthe quantity related to the rate of production of carbon dioxide.Methods 100 may include controlling the level (e.g., the concentration,the partial pressure, and/or the amount) of carbon dioxide in theatmosphere of the enclosure by directing the input stream through anumber of coiled ducts based at least in part upon the quantity relatedto the rate of production of carbon dioxide. Controlling may includecontrolling the rate of separation of carbon dioxide (or other highermolecular weight gas) in the coiled duct. Controlling may includemaintaining the carbon dioxide level (e.g., a concentration or a partialpressure) in the atmosphere of the enclosure below a threshold level.The threshold level may be a threshold deemed safe for human exposure,safe for human habitation, and/or comfortable to humans living withinthe enclosure. For example, controlling may include maintaining thepartial pressure of carbon dioxide in the atmosphere of the enclosure ata partial pressure of less than 1 kPa, less than 0.8 kPa, less than 0.6kPa, less than 0.4 kPa, less than 0.3 kPa, about 0.5 kPa, about 0.3 kPa,and/or about 0.2 kPa.

Examples of inventive subject matter according to the present disclosureare described in the following enumerated paragraphs.

A1. A centrifugal air separator comprising:

a separation section including a coiled duct, wherein the separationsection has an entrance port, an exit port, and a waste port; and

a drive section configured to direct an input air stream from anatmosphere of an enclosure into the entrance port, wherein theseparation section is configured to separate the input air stream into aclean air stream emitted from the exit port and a waste stream emittedfrom the waste port;

wherein the coiled duct has a duct entrance port fluidically connectedto the entrance port, a duct exit port fluidically connected to the exitport, and a duct waste port fluidically connected to the waste port;

wherein the coiled duct defines a channel between the duct entrance portand the duct exit port, wherein the duct waste port is proximate theduct exit port and fluidically connected to the channel;

wherein the separation section is configured to transmit through theduct entrance port a duct input air stream that is at least a portion ofthe input air stream and to at least partially separate the duct inputair stream according to a molecular weight of components of the ductinput air stream into a duct clean air stream that is at least a portionof the clean air stream and a duct waste stream that is at least aportion of the waste stream.

A2. The centrifugal air separator of paragraph A1, wherein theseparation section includes the input air stream at the entrance port,the clean air stream at the exit port, and the waste stream at the wasteport.

A3. The centrifugal air separator of any of paragraphs A1-A2, whereinthe coiled duct includes the duct input air stream at the duct entranceport, the duct clean air stream at the duct exit port, and the ductwaste stream at the duct waste port.

A4. The centrifugal air separator of any of paragraphs A1-A3, whereinthe waste stream is relatively enriched in higher molecular weightcomponents as compared to the clean air stream and optionally whereinthe higher molecular weight components include carbon dioxide.

A5. The centrifugal air separator of any of paragraphs A1-A4, whereinthe clean air stream is relatively depleted of higher molecular weightcomponents as compared to the waste stream and wherein the highermolecular weight components include carbon dioxide.

A6. The centrifugal air separator of any of paragraphs A1-A5, whereinthe clean air stream has a reduced concentration of gas having amolecular weight greater than 42 relative to the waste stream.

A7. The centrifugal air separator of any of paragraphs A1-A6, whereinthe clean air stream has a reduced concentration of carbon dioxiderelative to the waste stream.

A8. The centrifugal air separator of any of paragraphs A1-A7, whereinthe clean air stream has a lesser concentration of carbon dioxide thanthe input air stream.

A9. The centrifugal air separator of any of paragraphs A1-A8, whereinthe waste stream has a greater concentration of carbon dioxide than theinput air stream.

A10. The centrifugal air separator of any of paragraphs A1-A9, whereinthe waste stream has a reduced concentration of at least one of oxygen,nitrogen, and water vapor relative to the input air stream.

A11. The centrifugal air separator of any of paragraphs A1-A10, whereinthe channel is configured to flow the duct input air stream in agenerally laminar manner.

A12. The centrifugal air separator of any of paragraphs A1-A11, whereinthe centrifugal air separator is configured to flow the duct input airstream with a velocity of at least 10 m/s.

A13. The centrifugal air separator of any of paragraphs A1-A12, whereinthe centrifugal air separator is configured to flow the duct input airstream with a mass flow rate of at least 0.1 g/s or at least 0.5 g/s.

A14. The centrifugal air separator of any of paragraphs A1-A13, whereinthe centrifugal air separator is configured to flow the input air streamwith a mass flow rate of at least 0.5 g/s, at least 2 g/s, or at least 5g/s.

A15. The centrifugal air separator of any of paragraphs A1-A14, whereinthe coiled duct is configured to produce a pressure differential betweenthe duct entrance port and the duct exit port of less than 100 kPa, lessthan 60 kPa, or less than 30 kPa when the duct input air stream isflowing with a mass flow rate of 2.5 g/s.

A16. The centrifugal air separator of any of paragraphs A1-A15, whereinthe channel has an effective diameter that is substantially uniformalong the channel.

A17. The centrifugal air separator of any of paragraphs A1-A16, whereinthe channel has a profile that is substantially uniform along thechannel.

A18. The centrifugal air separator of any of paragraphs A1-A17, whereinthe channel has a profile that is at least one of substantiallycircular, substantially elliptical, substantially ovate, and rounded.

A19. The centrifugal air separator of any of paragraphs A1-A18, whereinthe channel includes at least one of a coiled portion, a spiral portion,and a helical portion.

A20. The centrifugal air separator of any of paragraphs A1-A19, whereinthe coiled duct has a series of loops.

A20.1. The centrifugal air separator of paragraph A20, wherein thecoiled duct has at least 5, at least 10, less than 50, and/or less than100 loops.

A20.2. The centrifugal air separator of any of paragraphs A20-A20.1,wherein the series of loops has an effective diameter that is one ofsubstantially uniform, tapered toward the duct entrance port, or taperedtoward the duct exit port.

A20.3. The centrifugal air separator of any of paragraphs A20-A20.2,wherein an average effective diameter of the series of loops is at least1, at least 2, at least 3, at least 5, at most 10, and/or at most 5times an average effective diameter of the channel.

A20.4. The centrifugal air separator of any of paragraphs A20-A20.3,wherein the series of loops is substantially helical.

A20.5. The centrifugal air separator of any of paragraphs A20-A20.4,wherein the loops of the series of loops are spaced apart from eachother, optionally by at least 0.1, at least 0.5, at least 1, at most 10,and/or at most 5 times an/the average effective diameter of the channel.

A21. The centrifugal air separator of any of paragraphs A1-A20.5,wherein the channel has an average effective diameter of at least 0.1cm, at least 0.2 cm, at least 0.5 cm, at least 1 cm, at most 100 cm, atmost 50 cm, at most 20 cm, at most 10 cm, at most 5 cm, and/or at most 2cm.

A22. The centrifugal air separator of any of paragraphs A1-A21, whereinthe duct waste port is fluidically connected to an end region of thechannel, wherein the end region comprises the duct exit port and one ofless than 20%, less than 10%, or less than 5% of a length of thechannel.

A23. The centrifugal air separator of any of paragraphs A1-A22, whereinthe duct waste port is fluidically connected to the channel within aleading edge region of the channel proximate the duct exit port, withinan outside edge region of the channel proximate the duct exit port,and/or between the leading edge region and the outside edge region.

A24. The centrifugal air separator of any of paragraphs A1-A23, whereinthe duct waste port has an effective diameter that is less than 50%,less than 20%, less than 10%, less than 3%, or less than 1% of aneffective diameter of the channel proximate the duct waste port.

A25. The centrifugal air separator of any of paragraphs A1-A24, whereinthe duct waste port has an effective diameter that is less than 50%,less than 20%, less than 10%, less than 3%, or less than 1% of aneffective diameter of the duct exit port.

A26. The centrifugal air separator of any of paragraphs A1-A25, whereinthe coiled duct is configured to emit the duct clean air stream and theduct waste stream at a mass flow ratio of the duct clean air stream tothe duct waste stream of at least 1:1, at least 2:1, at least 5:1, atleast 10:1, at least 100:1, or at least 1000:1.

A27. The centrifugal air separator of any of paragraphs A1-A26, whereinthe coiled duct includes a plurality of duct waste ports proximate theduct exit port.

A28. The centrifugal air separator of any of paragraphs A1-A27, whereinthe drive section is configured to direct the input stream from theentrance port through the separation section and/or the coiled duct.

A29. The centrifugal air separator of any of paragraphs A1-A28, whereinthe drive section is configured to drive air from the entrance port tothe exit port and/or to drive air from the duct entrance port to theduct exit port.

A30. The centrifugal air separator of any of paragraphs A1-A29, whereinthe drive section is configured to draw air from the entrance port tothe exit port and/or to draw air from the duct entrance port to the ductexit port.

A31. The centrifugal air separator of any of paragraphs A1-A30, whereinthe drive section includes a blower configured to direct the inputstream from the entrance port through the separation section.

A31.1. The centrifugal air separator of paragraph A31, wherein theblower is configured to drive air from the entrance port to the exitport and/or to drive air from the duct entrance port to the duct exitport.

A31.2. The centrifugal air separator of any of paragraphs A31-A31.1,wherein the blower is configured to draw air from the entrance port tothe exit port and/or to draw air from the duct entrance port to the ductexit port.

A32. The centrifugal air separator of any of paragraphs A1-A31.2,further comprising a waste collection body.

A32.1. The centrifugal air separator of paragraph A32, wherein the wastecollection body fluidically connects the duct waste port and the wasteport.

A32.2. The centrifugal air separator of any of paragraphs A32-A32.1,wherein the waste collection body is configured to direct the duct wastestream to the waste port.

A32.3. The centrifugal air separator of any of paragraphs A32-A32.2,wherein the waste collection body defines the waste port.

A32.4. The centrifugal air separator of any of paragraphs A32-A32.3,wherein the waste collection body forms a sheath over the coiled duct.

A32.5. The centrifugal air separator of any of paragraphs A32-A32.4,wherein the waste collection body substantially covers the coiled duct.

A32.6. The centrifugal air separator of any of paragraphs A32-A32.5,wherein the waste collection body defines a volume that contains atleast a portion of the coiled duct proximate the duct waste port.

A33. The centrifugal air separator of any of paragraphs A1-A32.6,further comprising a vacuum source coupled to the waste port.

A33.1. The centrifugal air separator of paragraph A33, wherein thevacuum source is configured to apply a sub-atmospheric pressure to thewaste port, optionally wherein the sub-atmospheric pressure is less than100 kPa, less than 80 kPa, less than 50 kPa, or less than 10 kPa.

A33.2. The centrifugal air separator of any of paragraphs A33-A33.1,wherein the vacuum source includes at least one of a vacuum pump and avacuum vessel.

A33.3. The centrifugal air separator of any of paragraphs A33-A33.2,wherein the vacuum source is configured to apply a negative pressuredifferential from the waste port to the channel proximate the wasteport, and optionally wherein the negative pressure differential has amagnitude of at least 10 kPa, at least 25 kPa, or at least 50 kPa.

A34. The centrifugal air separator of any of paragraphs A1-A33.3,wherein the separation section includes a plurality of coiled ducts.

A34.1. The centrifugal air separator of paragraph A34, wherein the drivesection is configured to direct air through the duct entrance port ofeach of the coiled ducts.

A34.2. The centrifugal air separator of any of paragraphs A34-A34.1,wherein the drive section is configured to drive air through each of thecoiled ducts, optionally from the respective duct entrance port to therespective duct exit port.

A34.3. The centrifugal air separator of any of paragraphs A34-A34.2,wherein the drive section is configured to draw air through each of thecoiled ducts, optionally from the respective duct entrance port to therespective duct exit port.

A34.4. The centrifugal air separator of any of paragraphs A34-A34.3,wherein the drive section includes a/the blower configured to direct airthrough the duct entrance port of each of the coiled ducts.

A34.4.1. The centrifugal air separator of paragraph A34.4, wherein theblower is configured to drive air through each of the coiled ducts,optionally from the respective duct entrance port to the respective ductexit port.

A34.4.2. The centrifugal air separator of any of paragraphsA34.4-A34.4.1, wherein the blower is configured to draw air through eachof the coiled ducts, optionally from the respective duct entrance portto the respective duct exit port.

A34.5. The centrifugal air separator of any of paragraphs A34-A34.4.2,wherein the coiled ducts are substantially identical.

A34.6. The centrifugal air separator of any of paragraphs A34-A34.5,further comprising an input manifold configured to substantially evenlysplit the input air stream into individual duct input air streams forthe coiled ducts.

A34.7. The centrifugal air separator of any of paragraphs A34-A34.6,further comprising an output manifold configured to combine the ductclean air streams of the coiled ducts into the clean air stream.

A34.8. The centrifugal air separator of any of paragraphs A34-A34.7,further comprising a/the waste collection body configured to combine theduct waste streams into the waste stream.

A35. The centrifugal air separator of any of paragraphs A1-A34.8,further comprising:

a second-stage section including a second-stage coiled duct, wherein thesecond-stage section has a second-stage entrance port, a second-stageexit port, and a second-stage waste port, wherein the waste port isfluidically connected to the second-stage entrance port, wherein thesecond-stage section is configured to separate the waste stream into asecond-stage clean air stream emitted from the second-stage exit portand a second-stage waste stream emitted from the second-stage wasteport;

wherein the second-stage coiled duct has a second-stage duct entranceport fluidically connected to the second-stage entrance port, asecond-stage duct exit port fluidically connect to the second-stage exitport, and a second-stage duct waste port fluidically connected to thesecond-stage waste port;

wherein the second-stage coiled duct defines a second-stage channelbetween the second-stage duct entrance port and the second-stage ductexit port, wherein the second-stage duct waste port is proximate thesecond-stage duct exit port and fluidically connected to thesecond-stage channel;

wherein the second-stage section is configured to transmit through thesecond-stage duct entrance port a second-stage duct input air streamthat is at least a portion of the waste stream and to at least partiallyseparate the second-stage duct input air stream according to a molecularweight of components of the second-stage duct input air stream into asecond-stage duct clean air stream that is at least a portion of thesecond-stage clean air stream and a second-stage duct waste stream thatis at least a portion of the second-stage waste stream.

A35.1. The centrifugal air separator of paragraph A35, wherein thesecond-stage section has any of the features of the separation sectionof any of paragraphs A1-A34.8.

A35.2. The centrifugal air separator of any of paragraphs A35-A35.1,wherein the second-stage section includes a blower to direct the wasteair stream from the waste port toward the second-stage exit port.

A36. The centrifugal air separator of any of paragraphs A1-A35.2,further comprising a carbon dioxide sensor configured to sense at leastone of a concentration and a partial pressure of carbon dioxide in atleast one of the atmosphere of the enclosure, the input air stream, theclean air stream, and the waste stream.

A37. The centrifugal air separator of any of paragraphs A1-A36, furthercomprising a controller.

A37.1. The centrifugal air separator of paragraph A37, wherein thecontroller is programmed to control air flow through centrifugal airseparator, optionally based upon at least one of a concentration and apartial pressure of carbon dioxide in at least one of the atmosphere ofthe enclosure, the input air stream, the clean air stream, and the wastestream.

A37.2. The centrifugal air separator of any of paragraphs A37-A37.1,wherein the controller is programmed to control a rate of carbon dioxideseparation in the centrifugal air separator.

A37.3. The centrifugal air separator of any of paragraphs A37-A37.2,wherein the controller is programmed to maintain a level of carbondioxide in the atmosphere of the enclosure at a partial pressure of lessthan 1 kPa, less than 0.8 kPa, less than 0.6 kPa, less than 0.4 kPa,less than 0.3 kPa, about 0.5 kPa, about 0.3 kPa, and/or about 0.2 kPa.

A37.4. The centrifugal air separator of any of paragraphs A37-A37.3,wherein the controller is programmed to perform the method of any ofparagraphs B1-B6.

A38. A life support system to support mammals living in an enclosure,the life support system comprising:

the centrifugal air separator of any of paragraphs A1-A37.4.

B1. A method of recirculating clean air in an atmosphere of anenclosure, the method comprising:

directing an input air stream from the atmosphere of the enclosurethrough a coiled duct at a rate sufficient to stratify the input airstream within the coiled duct according to a molecular weight ofcomponents of the input air stream and to form a heavy fraction streamand a light fraction stream, wherein the heavy fraction stream isrelatively enriched in carbon dioxide as compared to the light fractionstream;

withdrawing the heavy fraction stream from the coiled duct; and

returning the light fraction stream from the coiled duct to theatmosphere of the enclosure.

B2. The method of paragraph B1, wherein the directing includes directingthe input air stream through the centrifugal air separator of any ofparagraphs A1-A37.3.

B3. The method of any of paragraphs B1-B2, further comprising sensing atleast one of a concentration and a partial pressure of carbon dioxide inat least one of the atmosphere of the enclosure, the input air stream,the heavy fraction stream, and the light fraction stream.

B4. The method of any of paragraphs B1-B3, further comprisingdetermining a quantity related to a rate of production of carbon dioxidewithin the enclosure and controlling a level of carbon dioxide in theatmosphere of the enclosure by directing the input air stream through anumber of coiled ducts based at least in part upon the quantity, andoptionally selecting the number of coiled ducts based at least in partupon the quantity, wherein the level is at least one of a concentration,a partial pressure, and an amount.

B4.1. The method of paragraph B4, wherein the quantity is selected fromthe group consisting of a number of people within the enclosure, a levelof carbon dioxide in the atmosphere of the enclosure, a level of carbondioxide in the input air stream, a level of carbon dioxide in the heavyfraction stream, a level of carbon dioxide in the light fraction stream,and the rate of production of carbon dioxide within the enclosure.

B4.2. The method of any of paragraphs B4-B4.1, wherein the controllingincludes maintaining a partial pressure of carbon dioxide in theatmosphere of the enclosure at a partial pressure of less than 1 kPa,less than 0.8 kPa, less than 0.6 kPa, less than 0.4 kPa, less than 0.3kPa, about 0.5 kPa, about 0.3 kPa, and/or about 0.2 kPa.

B5. The method of any of paragraphs B1-B4.2, further comprisingaccumulating the heavy fraction stream.

B6. The method of any of paragraphs B1-B5, further comprising directingthe heavy fraction stream out of the enclosure.

As used herein, the terms “selective” and “selectively,” when modifyingan action, movement, configuration, or other activity of one or morecomponents or characteristics of an apparatus, mean that the specificaction, movement, configuration, or other activity is a direct orindirect result of user manipulation of an aspect of, or one or morecomponents of, the apparatus.

As used herein, the terms “adapted” and “configured” mean that theelement, component, or other subject matter is designed and/or intendedto perform a given function. Thus, the use of the terms “adapted” and“configured” should not be construed to mean that a given element,component, or other subject matter is simply “capable of” performing agiven function but that the element, component, and/or other subjectmatter is specifically selected, created, implemented, utilized,programmed, and/or designed for the purpose of performing the function.It is also within the scope of the present disclosure that elements,components, and/or other recited subject matter that is recited as beingadapted to perform a particular function may additionally oralternatively be described as being configured to perform that function,and vice versa. Similarly, subject matter that is recited as beingconfigured to perform a particular function may additionally oralternatively be described as being operative to perform that function.Further, as used herein, the singular forms “a”, “an” and “the” may beintended to include the plural forms as well, unless the context clearlyindicates otherwise.

The various disclosed elements of systems and steps of methods disclosedherein are not required of all systems and methods according to thepresent disclosure, and the present disclosure includes all novel andnon-obvious combinations and subcombinations of the various elements andsteps disclosed herein. Moreover, any of the various elements and steps,or any combination of the various elements and/or steps, disclosedherein may define independent inventive subject matter that is separateand apart from the whole of a disclosed apparatus or method.Accordingly, such inventive subject matter is not required to beassociated with the specific systems and methods that are expresslydisclosed herein, and such inventive subject matter may find utility insystems and/or methods that are not expressly disclosed herein.

As used herein, the phrase, “for example,” the phrase, “as an example,”and/or simply the term “example,” when used with reference to one ormore components, features, details, structures, embodiments, and/ormethods according to the present disclosure, are intended to convey thatthe described component, feature, detail, structure, embodiment, and/ormethod is an illustrative, non-exclusive example of components,features, details, structures, embodiments, and/or methods according tothe present disclosure. Thus, the described component, feature, detail,structure, embodiment, and/or method is not intended to be limiting,required, or exclusive/exhaustive; and other components, features,details, structures, embodiments, and/or methods, including structurallyand/or functionally similar and/or equivalent components, features,details, structures, embodiments, and/or methods, are also within thescope of the present disclosure.

As used herein, the phrases “at least one of” and “one or more of,” inreference to a list of more than one entity, means any one or more ofthe entities in the list of entities, and is not limited to at least oneof each and every entity specifically listed within the list ofentities. For example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently, “at least one of A and/or B”)may refer to A alone, B alone, or the combination of A and B.

The invention claimed is:
 1. A centrifugal air separator comprising: aseparation section including a coiled duct, wherein the separationsection has an entrance port, an exit port, and a waste port; and adrive section including a blower, wherein the drive section isconfigured to direct an input air stream from an atmosphere of anenclosure into the entrance port, wherein the blower is configured todirect the input air stream through the separation section, wherein theseparation section is configured to separate the input air stream into aclean air stream emitted from the exit port and a waste stream emittedfrom the waste port; wherein the coiled duct has a duct entrance portfluidically connected to the entrance port, a duct exit port fluidicallyconnected to the exit port, and one or more duct waste ports fluidicallyconnected to the waste port; wherein the coiled duct defines a channelbetween the duct entrance port and the duct exit port, wherein all ductwaste ports are proximate the duct exit port and fluidically connectedto the channel; wherein the separation section is configured to transmitthrough the duct entrance port a duct input air stream that is at leasta portion of the input air stream and to at least partially separate theduct input air stream according to a molecular weight of components ofthe duct input air stream into a duct clean air stream that is at leasta portion of the clean air stream and a duct waste stream that is atleast a portion of the waste stream.
 2. The centrifugal air separator ofclaim 1, wherein the waste stream is relatively enriched in carbondioxide as compared to the clean air stream.
 3. The centrifugal airseparator of claim 1, wherein the duct waste ports are within a leadingedge region of the coiled duct proximate the duct exit port.
 4. Thecentrifugal air separator of claim 1, wherein the coiled duct has aseries of loops, wherein an average diameter of the series of loops isat least 1 and at most 5 times an average diameter of the channel. 5.The centrifugal air separator of claim 1, wherein the coiled duct has aseries of at least 10 loops.
 6. The centrifugal air separator of claim1, wherein the channel has an average diameter of at least 0.1 cm and atmost 10 cm.
 7. The centrifugal air separator of claim 1, wherein theblower is configured to drive air from the duct entrance port to theduct exit port.
 8. The centrifugal air separator of claim 1, wherein thecentrifugal air separator is configured to flow the duct input airstream with a velocity of at least 10 m/s.
 9. The centrifugal airseparator of claim 1, wherein the centrifugal air separator isconfigured to flow the duct input air stream with a mass flow rate of atleast 0.1 g/s.
 10. The centrifugal air separator of claim 1, wherein thecoiled duct is configured to produce a pressure differential between theduct entrance port and the duct exit port of less than 30 kPa when theduct input air stream is flowing with a mass flow rate of 2.5 g/s. 11.The centrifugal air separator of claim 1, wherein each of the duct wasteports has a diameter that is less than 10% of a diameter of the channelat the duct exit port.
 12. The centrifugal air separator of claim 1,wherein the coiled duct is configured to emit the duct clean air streamand the duct waste stream at a mass flow ratio of the duct clean airstream to the duct waste stream of at least 100:1.
 13. The centrifugalair separator of claim 1, further comprising a waste collection bodythat fluidically connects the duct waste ports and the waste port. 14.The centrifugal air separator of claim 1, further comprising a vacuumsource coupled to the waste port.
 15. The centrifugal air separator ofclaim 1, wherein the separation section includes a plurality of coiledducts and wherein the drive section is configured to direct air throughthe duct entrance port of each of the coiled ducts.
 16. A life supportsystem to support mammals living in an enclosure, the life supportsystem comprising: a carbon dioxide sensor configured to sense a partialpressure of carbon dioxide in an atmosphere of the enclosure; acentrifugal air separator including: a separation section including aplurality of coiled ducts, wherein the separation section has anentrance port, an exit port, and a waste port; a drive section includinga blower, wherein the drive section is configured to direct an input airstream from the atmosphere of the enclosure into the entrance port,wherein the blower is configured to direct the input air stream throughthe separation section, wherein the separation section is configured toseparate the input air stream into a clean air stream emitted from theexit port and a waste stream emitted from the waste port; wherein eachcoiled duct has a duct entrance port fluidically connected to theentrance port, a duct exit port fluidically connected to the exit port,and one or more duct waste ports fluidically connected to the wasteport; wherein each coiled duct defines a channel between the ductentrance port and the duct exit port, wherein all duct waste ports areproximate the duct exit port and fluidically connected to the channel;wherein the separation section is configured to transmit through eachduct entrance port a duct input air stream that is a portion of theinput air stream, wherein each coiled duct is configured to at leastpartially separate the duct input air stream according to a molecularweight of components of the duct input air stream into a duct clean airstream that is a portion of the clean air stream and a duct waste streamthat is a portion of the waste stream; and a waste collection body thatfluidically connects the duct waste ports of the coiled ducts with thewaste port; and a controller programmed to maintain a level of carbondioxide in the atmosphere of the enclosure at a partial pressure of lessthan 1 kPa by controlling air flow through the centrifugal air separatorbased upon the level of carbon dioxide in the atmosphere of theenclosure.
 17. The life support system of claim 16, wherein thecentrifugal air separator is configured to flow the input air streamwith a mass flow rate of at least 0.5 g/s.
 18. The life support systemof claim 16, wherein each duct waste port is within a leading edgeregion of the respective coiled duct proximate the respective duct exitport.
 19. The life support system of claim 16, wherein each coiled ducthas a series of at least 10 loops, wherein an average diameter of theseries of loops is at least 1 and at most 5 times an average diameter ofthe channel of the respective coiled duct.
 20. A method of recirculatingclean air in an atmosphere of an enclosure, the method comprising:directing an input air stream from the atmosphere of the enclosurethrough a centrifugal air separator that includes a number of coiledducts at a rate sufficient to stratify the input air stream within eachcoiled duct according to a molecular weight of components of the inputair stream and to form a heavy fraction stream and a light fractionstream, wherein the heavy fraction stream is relatively enriched incarbon dioxide as compared to the light fraction stream; withdrawing theheavy fraction stream from the number of coiled ducts; returning thelight fraction stream from the number of coiled ducts to the atmosphereof the enclosure; determining a quantity related to a rate of productionof carbon dioxide within the enclosure; and maintaining a level ofcarbon dioxide in the atmosphere of the enclosure at a partial pressureof less than 1 kPa by selecting the number of coiled ducts based atleast in part upon the quantity; wherein the centrifugal air separatorincludes: a separation section including a plurality of coiled ductsthat includes the number of coiled ducts, wherein the separation sectionhas an entrance port, an exit port, and a waste port; and a drivesection including a blower, wherein the drive section is configured todirect the input air stream from the atmosphere of the enclosure intothe entrance port, wherein the blower is configured to direct the inputair stream through the separation section, wherein the separationsection is configured to separate the input air stream into the lightfraction stream emitted from the exit port and the heavy fraction streamemitted from the waste port; wherein each coiled duct of the pluralityof coiled ducts has a duct entrance port selectively fluidicallyconnected to the entrance port, a duct exit port fluidically connectedto the exit port, and one or more duct waste ports fluidically connectedto the waste port; wherein each coiled duct of the plurality of coiledducts defines a channel between the duct entrance port and the duct exitport, wherein all duct waste ports are proximate the duct exit port andfluidically connected to the channel; wherein the separation section isconfigured to transmit through each duct entrance port of the pluralityof coiled ducts a duct input air stream that is at least a portion ofthe input air stream, wherein each coiled duct of the plurality ofcoiled ducts is configured to at least partially separate the duct inputair stream according to a molecular weight of components of the ductinput air stream into a duct light fraction stream that is at least aportion of the light fraction stream and a duct heavy fraction streamthat is at least a portion of the heavy fraction stream.